Designs of ultrasonic liquid level detectors are known where resonators and tuning forks are driven with the help of sound waves. The acoustic parameters of resonators and tuning forks vary when contacting liquid, a medium with higher density than air, and these variations are detected.
The design according to DE patent N 4201360 can serve as an example. The device contains two or more vibratory rods put into a reservoir under control, which are connected with radiating and receiving transducers. The same principle is used with the "Device for detection and/or control of filled reservoir level," according to DE patent N 4118793, or the "Device for measurement and/or keeping of given level in a reservoir," according to the International application WO 92/21945.
The given designs of the liquid level detectors depend on operating conditions. Liquid and dirt remaining in the tuning fork spaces can influence measurement accuracy of the mentioned devices.
A device for liquid level detection is known from DE patent N 3011603 priority 26.03.80, Int. Cl. G 01 F 23/28. The device contains vibratory elements placed co-axially. The space between the vibratory elements is isolated from the medium and is located along the whole length of the rod. Piezoelements are fixed on membrane inserts connected to one of the vibrators. The case of the device is fixed to the membrane insert. The attachment joint of the device case to the external basement is made in the form of a threaded connection. The device differs from the offered invention in operating principle and design.
A further device for liquid level control is known from DE application N 2949162 priority 06.12.79 Int. Cl. G 01 F 23/28. The device has a hollow portion along the whole length of a waveguide, to which a radiator and receiver are fixed in different places. The case is not rigidly fixed to the waveguide and includes a threaded connection for fixing it to the external base.
Moreover an acoustic liquid level detector is known from FR application N 2596515 priority 28.03.86 Int. Cl. G 01 F 23/28. The detector contains a hollow rod along the entire length and is open to the surrounding medium. Another hollow pattern along the length of the waveguide is installed inside the rod on which transducers are installed. The waveguide attachment points to the external base are not considered in this design.
An ultrasonic liquid level indicator is known from SU Invenitor's Certificate N 231151, wherein the detector consists of two separated waveguides. The waveguides are fixed in the walls of a reservoir under control of the oscillation nodes.
The designs of all above mentioned ultrasonic detectors differ from the offered one. In particular, protection from the influence of condensate, any remaining liquid and dirt on measurement accuracy is not provided in the above designs.
The "Detector of Liquid Presence" according to EP patent N 409732 priority 19.07.90 Int. CL. G 01 F 23/28 is the closest in technical principle. The design of the detector includes a case, a measuring element connected with a pulse generator and a receiving device. The measuring element of this device includes an acoustical-electrical transducer and a compound acoustic waveguide connected to the transducer. The first part of the compound acoustic waveguide consists of a solid cylinder and the second one consists of a hollow cylinder. The first part of the waveguide is smaller in diameter than the second one.
The performance accuracy of the given detector design depends on conditions of the surrounding medium. Liquid and other contaminates can accumulate in the open space. Liquid and dirt can also gather on the transducer and on the waveguide case where the junction (transition) to a greater diameter occurs. All these can influence the accuracy of the detector performance.